Although Mercedes and Red Bull have yet to attempt qualifying-style runs themselves, it was an ominous benchmark.

Valtteri Bottas, who last week admitted Ferrari held an early advantage over Mercedes and Red Bull, isn't changing his opinion at Test Two despite the world champions' significant aerodynamic overhaul of their new car.

"Between us [and Red Bull], the differences are not massive," the Mercedes driver told reporters. "But our feeling is that Ferrari are a bit ahead of us."

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A look back at Sebastian Vettel's crash from the third day of the second test which hampered the team's running

A look back at Sebastian Vettel's crash from the third day of the second test which hampered the team's running

A cautious Bottas added to Sky Sports News: "I think we need to unlock more from the new package to be able to compete with them properly."

Red Bull also believe they are playing catch-up.

When asked if they could have matched the Ferrari time, Pierre Gasly admitted: "Honestly, no. To be fair, they are really fast and showed some good pace."

Ferrari: We can go fasterAlthough the pecking order in pre-season can prove misleading, Thursday offered compelling evidence that Ferrari are, so far at least, F1 2019's team to beat.

In a warning to the rest of the field, Leclerc admitted he was not even at full tilt when he posted his eye-catching time - which was faster than Ferrari managed in Spanish GP qualifying last year, albeit on softer tyres.

"We are not flat out," the Monegasque said. "There's still some margin but it's looking good for now."

Leclerc set personal best after personal best in a pre-lunch blitz in Barcelona, lighting the screens purple while Mercedes and Red Bull stuck to their testing programme.

Mercedes plan to up their pace with short runs on Friday, the final day of track action before the season-opener in Australia.

"I think we are looking strong at the moment," continued Leclerc. "Whether they are sand-bagging more, or less, we don't know and we will only know in Melbourne qualifying.

"But for now we are pretty happy with the job we are doing."

Mercedes improving, but is it enough?While Mercedes didn't complete the typical low-fuel run on Thursday, Lewis Hamilton did set his fastest time, 1:18.097, on the second hardest tyre available, the Compound 2.

And there is also firm belief that Mercedes have made a big step with their heavily-revised W10, which has several new aerodynamic parts compared to last week's car.